The present disclosure refers in general to electric and/or hybrid vehicles. More specifically, the disclosure relates to a device and a method for measuring isolation resistance of battery powered systems, preferably applicable for measuring isolation or leakage resistance in electric vehicles and/or hybrid vehicles.
An object of the invention is to provide effective isolation resistance measurements, with high accuracy regardless of battery voltage variations.
Electric and hybrid vehicles include high-voltage batteries, typically with a nominal voltage within the range 300-600 volts, that are used to power an electrical motor.
The high-voltage battery is electrically insulated from the body of the vehicle, that is, the vehicle chassis, whereas the negative battery pole in the low-voltage system of the vehicle is connected to chassis ground as is common in vehicles.
It is desirable to keep the two voltage systems separated, and to keep the high-voltage system electrically isolated from chassis ground. In order to detect faults in the high-voltage system, such as an isolation fault, the insulation of the high-voltage system may be continuously monitored to detect leakages in the high-voltage insulation.
Many conventional power systems utilize some means to protect the system against faults, such as line-to-line and line-to-ground faults.
A known method for measuring isolation resistances, is described in the US Standard FMVSS 305: Electric powered vehicles. Electrolyte spillage and electrical shock protection; 11 Sep. 2008. However, the accuracy of the system described in that standard does not consider a measurement circuit to calculate the isolation resistances, and the accuracy of the system is not satisfactory. In addition the system described in that Standard does not consider voltage variations of the high-voltage DC source.
Therefore, there is the need in this technical field, to improve accuracy in the isolation resistance measurements and regardless of battery voltage variations.